1. Field of the Invention
This invention relates to the comminution of wood and more particularly to a spiral shear mechanism which, through its self-feeding characteristic, pulls wood through an apparatus while simultaneously severing particles of engineered length and cross-sectional area.
2. Description of the Prior Art.
Structural particleboard is expected to come into widespread use in the construction industry in the future. This product obtains its stiffness and stability from the long narrow flakes of minimal thickness of which it is comprised. Production of these long, thin flakes has presented problems since previous art could not provide controlled length particles needed for feed into flaking machines. Conventional wood chipping machines have been used to cut chips from logs which are then fed into a ring-type flaker to be cut to the proper thickness. Wood chippers are ordinarily used to produce relatively short, small chips for pulping processes. These short chips of which only 50-60 percent are to the length setting provided in the chipper do not produce the quality flake needed for structural strength board. The present invention can produce long wood pieces, or "fingerlings," of which 90-95 percent will be of sufficient length to be fed through flaker and then used for structural particleboard.
Presently a disk-type flaker is used which also can produce a high percentage of usable long particles. This flaker takes clean, round logs and cuts them into flakes of the desired size, thus eliminating the extra step necessary when using a ring-type flaker. The present invention, however, has many advantages over the disk flaker. The roundwood which the disk flaker requires as its raw material is not typical of the forest residue which is used for particleboard. The small, crooked material which is not suited for the disk flaker can be easily converted into fingerlings by the present invention. Furthermore, due to its small bulk and weight, the spiral cutter can be brought into the woods and operated at the forest residue collection site. This eliminates the problems involved in transporting bulky forest residue and prevents waste of the smaller branches which might otherwise be left at the site. Alternatively, this machine can reduce logging residue into pieces for dispersal over the forest floor with the benefit of rapid decay.
Another advantage over the prior art is that this invention provides positive control to cut fingerlings in the direction of the grain so that the resulting flakes will have the grain running lengthwise. This provides much greater strength than where the grain is cut cross-wise, which may result when a conventional chipper is used.
This invention can also be used to provide pulp chips of uniform length for papermaking. It is desirable that chips for this use be of very consistant dimensions. The reason for this is because chips of unequal size will cook at different rates in the pulping processes. As a consequence, when the wood chipper provides chips of varying sizes, the smaller chips will be overcooked reducing the quantity of usable fiber.
Normally this apparatus will be used to produce small particle of lengths between 1-inch and 6-inches, but it does have the capability of producing longer pieces of wood for such purposes as firewood. This is an advantage which no previous wood chipper can claim.
The helical shear cutter has fewer moving parts than wood chippers of the prior art and therefore lasts longer and requires less maintenance. When blade sharpening is necessary it is a simple operation because it may be done while the blade is mounted on the machine. Conventional chippers require removal of the blades for sharpening which can be a very costly procedure.